Here’s a really fascinating article in Inside GNSS about the proliferation of electronic countermeasures against GPS. The heaviest users are lorry drivers, who use GPS jammers to disrupt management surveillance of their working day. I would guess that this has probably benefited from an existing culture of radar detectors, GATSO databases, and such.
This causes curious side effects, notably where major motorways are close to airport runways for which a GPS-based nonprecision approach is published (the authors propose various algorithms), and in financial districts where high-frequency trading systems require very accurate timing. This results in a large concentration of tier-1 NTP servers fed by GPS receivers, that get disrupted on a regular basis by a delivery van using a jammer.
Another interesting use case that comes to mind is Google’s NewSQL, globally distributed, column-based data store, Spanner, which relies for its versioning-based consistency guarantee on very accurate timing typically derived at each location from multiple GPS receivers. The Googlers did build in cross-checks between sites, not being dumb or anything, so there are limits to how much weirdness it could cause.
The devices cost a few dozen galactic credits a go. Inside GNSS points out that they are advertised on the basis of how much Tx power they crank out, which isn’t ideal as the GPS signal is very diffuse at this distance from high earth orbit, and any more than the minimum power to drown it out both buggers it up for others and increases your chances of being detected.
I feel I should point out that Charlie Stross actually suggested this solution, or actually a somewhat more advanced one more like this, in comments right here on this blog as a way of defeating Alistair Darling’s national road-pricing system. Sadly, even Google search can’t find it in the old enetation comments system.
Meanwhile, in Keighley:
Mrs Orchard, of Denholme Gate, said shortly after her sick leave started, odd phone calls were made to the family home by people asking if she could do some work for them, her family and neighbours saw men hiding in cars outside her home, and then she found a GPS tracker had been attached to the underside of her Audi car.
I am slightly surprised that the GPS jammers actually work. Not work in the sense that they block the GPS signal – of course they can do that – but work in the sense of allowing the truckers to skive off without arousing suspicion. When they turn in a completely blank GPS record at the end of the week, doesn’t that arouse suspicion?
Perhaps the point is to increase the number of breaks in the record to a level where “did you follow the prescribed route?” or “did you have your tea at 10.37 exactly?” are essay questions rather than yes/no.